1. Field of the Invention
The present invention relates to wireless local area networks including handheld computers that communicate with each other and with central computers using RF communications signals, and more particularly, to an optical interface provided on a printer and on a handheld computer to permit direct data communication therebetween as well as wireless communication between the printer and other elements of the wireless local area network.
2. Description of Related Art
In the automated identification and data capture industry, it is known to operate a wireless local area network (LAN) that includes a plurality of handheld data-collection terminals that communicate over a radio frequency (RF) channel with a central host computer. The data-collection terminals enable an operator to scan and decode data that may be encoded in the form of a one or two-dimensional bar code symbology. The decoded information is then transmitted back to the central host computer across the RF channel. Such wireless LAN systems are particularly well suited to data capture applications as diverse as process and inventory control, time and attendance monitoring, security management, customer service and point of sale recording, shipping and receiving record keeping, and warehouse operations.
The handheld data-collection terminals generally have limited functionality in order to keep their size, weight and cost to a minimum. In recent years, however, the availability of high performance microprocessors and other integrated electronic systems has driven a demand for more sophisticated data-collection terminals which have all the power of personal computers in a palm-sized package. These data-collection computers may include integrated scanning systems using charge-coupled device (CCD) elements to form a memory-mapped image of a region of interest, as well as advanced processing capability to locate, orient and decode the memory-mapped image into the information that corresponds to the bar code symbol. For example, the higher processing power of the data-collection computers permits better error correction, enabling collection of bar code symbols having readability problems, such as a torn, soiled or partially obliterated bar code symbol. As a result, the data-collection computers are better able to decode bar code symbols than the less sophisticated data-collection terminals.
The wireless LAN may further include one or more printers for producing bar code labels used in identifying items that are tracked in a particular data capture application. In order for the data-collection terminal to accurately read the bar code symbol, it is essential that the symbol be printed in a high quality manner, without any streaking, blurring or improper registration of the symbols to the labels. At the same time, it is essential that the adhesive backing layer of the labels not be damaged by heat generated during the printing process. In view of the demanding printing requirements, bar code symbols are often printed using direct thermal or thermal transfer printing techniques, referred to collectively herein as thermal printing. To achieve maximum data throughput, dedicated thermal printers are generally coupled directly to the central host computer unit through a hard-wired communication link. The printers may further be located in a climate controlled environment that is otherwise isolated from the rest of the LAN.
From time to time, it becomes necessary for a data-collection computer to communicate directly to a printer, rather than through the LAN. For example, a test batch configuration may be stored in memory within a data-collection computer and loaded directly into one or more printers to insure uniform print results (referred to as "cloning"). Alternatively, an operator of a data-collection computer in a large facility may wish to utilize a local printing station disposed in near proximity to a work location rather than returning to a central printing station adjacent to the central host computer. In these situations, the operator may opt to connect the data-collection computer to the printer using conventional printer cables having standard interface connectors, e.g., an RS-232 connector and the like.
Despite the advantages of coupling the data-collection computer to the printer, there are numerous operational difficulties that make such a connection impractical. First of all, the operator may not always be able to locate a suitable interface cable, and it is often time consuming and cumbersome to connect the cable to an interface panel of the printer. Repeated connection and disconnection of interface cables tends to weaken the connectors of the printer and data-collection computer, resulting in intermittent electrical connections.
Even more significant is the threat of harm to either of the printer or the data-collection computer due to effects such as electro-static discharge (ESD) or electromagnetic interference (EMI). ESD refers to sparks or electrons that jump from an electrically charged object to an approaching conductive object. EMI refers to electromagnetic waves that emanate from an electrical device, including both low-frequency waves from electro-mechanical devices and high-frequency waves (RFI) from electronic circuit chips and other electronic devices. Any ESD which results from the coupling of the interface cable between the printer and the data-collection computer can damage the delicate electronic circuitry of either of the two systems. Moreover, EMI from an unshielded or poorly shielded interface cable can interfere with the operation of the printer or the data-collection computer, resulting in further damage or degradation of system performance.
Accordingly, it would be desirable to provide a convenient method and apparatus to permit a printer to communicate with a handheld data-collection computer without requiring interface cables. Such a system would eliminate the inconvenience and risks associated with use of such interface cables.